This invention relates to a continuous process for obtaining optimal separation of a fluid mixture by sorption. The method also relates to a process for preparing precise fluid mixtures where the metered component is mixed by moving boundary sorption.
In recent years, cyclic separation processes have received considerable attention. Such processes as pressure-swing adsorption, parametric pumping, and cycling zone adsorption, separate continuous or semi-continuous fluid feed streams by cycling a thermodynamic variable which affects the mass transfer of fluid components with a sorption media. The cycle is designed to alternately sorb and desorb components so the fluid components are separated and the media returns to its initial condition after the completion of a cycle. The feed and product streams can be rendered continuous by combining sorption units in parallel but each unit necessarily experiences discontinuous flow conditions so that the sorbing media can be altered by changing thermodynamic variables such as temperatures, pH, or pressure, for example, and so that the other product stream can be created thereby. The discontinuity of flow through or past the sorbing media creates inefficiency in the separations because of the mixing of fluid elements that have been exposed to the sorbing media under different conditions.
All practical separation techniques that occur with discontinuous flow result in product reservoir mixing. Since the feed mixture flows through the vessel during the sorption cycle of the cycling process, the sorbent will fill with the sorbed fluid component and the sorptivity will decrease. Thus, fluid entering the vessel early in the cycle is stripped of the sorbable constitutents to a greater extent than fluid entering late in the cycle. As a reult, the composition of the fluid emerging from the sorbent zone is continually changing. Such a system cannot be controlled as efficiently as a single condition, continuous, time invariant process because in the cyclic operation you must compromise between optimizing for the early portion of the sorption cycle and the later portion. The ideal situation where product flow streams are not mixed would require a prohibitively large number of separate reservoirs as well as a complicated flow management system.
It is an object of the present invention to provide a method for continuous flow separation or mixing which avoids the inefficiencies inherent in reservoir mixing. It is a further object of the present invention to provide a continuous method of flow separation or mixing wherein only a significant part of the seal between the sorption and desorption zones is the sorption media itself.